Battery packs for use in mobile devices are moving towards higher performance, and particularly, their capacity to volume is gradually increasing.
However, portable devices, for example, smart phones or laptop computers, which becomes smaller but move towards diversity in function and a higher data processing rate, consume a greater amount of power, thereby it difficult to ensure a sufficient usage time with only one battery pack.
Accordingly, carrying at least two charged battery packs is needed, and in this case, to charge the respective battery packs, the battery packs are mounted on an electronic appliance body or a charger holder, and when connected to a charger, are charged.
However, mounting a plurality of battery packs on an electronic appliance body or a charger holder and then charging them individually may be very tedious. Furthermore, users have to repeatedly perform an operation of connecting a battery pack to a charger after a previous battery pack is fully charged, and inconveniently, during the operation, the users cannot do other task or sleep.
Therefore, in the charging of battery packs, there is a need for development of a battery pack having a structure that allows it to be charged by a direct connection to a charger without being mounted on an electronic appliance or a charger holder and that allows concurrent charging of a plurality of battery packs by interconnection of the battery packs.